The present invention relates generally to motor clutch drive systems and more specifically to such drive systems which include fluid actuated oil shear type clutch units for operatively connecting a driving motor to apparatus to be driven thereby and associated control apparatus for selectively controlling the application of actuating fluid to the clutch unit.
In numerous applications it is highly desirable to be able to smoothly accelerate a driven apparatus from a static condition to full operating speed without subjecting the apparatus to the often excessive stress and strain associated with an uneven or abrupt start. Counteracting this desire to achieve a smooth gradual startup of the driven apparatus is the desire to achieve full speed operation as rapidly as possible as well as the desire to avoid any excessive wear resulting from unnecessarily prolonged slippage of the clutch unit as it is being engaged.
Additionally, smooth startups may be particularly desirable in apparatus having multiple spaced drives provided thereon such as for example overland conveyor systems utilized in various types of mining operations so as to avoid shifting or spillage of the load thereon as well as to avoid excessive tensioning of the conveyor belt and the potential backlash which may result. In such conveyor systems it is normally necessary to progressively start the various drives in succession with a slight delay between each successive start so as to enable the sections of conveyor belt between each of the drives to be properly tensioned. The application of driving forces by proper clutch actuation so as to achieve a soft start enables the conveyor belt to tension in a generally even manner whereby any backlash or rebounding thereof is minimized. In order to insure such proper tensioning of the conveyor system, it is important that the acceleration curves of each drive unit be consistent, predictable and very accurately controllable.
Additionally, because the clutch actuating controls must be located in close proximity to the drive units and hence the conveyor equipment, they are subjected to extremely adverse operating conditions due to the high level of contaminants in the surrounding atmosphere. This problem is particularly prevalent in systems used for transporting coal both at the mines and at coal fired power plants. As a result, problems have been encountered as a result of dirt contamination of clutch actuating fluid causing plugging of control valves thereby resulting in loss of full operating control as well as increased maintenance cost and equipment downtime. Therefore, it is highly desirable to provide control valving which is substantially less sensitive to such dirt contamination.
The present invention provides a drive system particularly well suited for providing very smooth and yet rapid acceleration of driven apparatus both in terms of single and multiple drive units. The drive system includes an improved cam type control valve which is extremely resistant to operation degradation as a result of contaminants in the actuating fluid and which operates reliably to apply actuating fluid to the clutch unit in accordance with a predetermined profile so as to smoothly bring the driven apparatus up to full operating speed within a minimum amount of time and with a minimum amount of clutch slippage. The control valve is designed to be driven through a plurality of steps by a stepping motor and associated control circuitry whereby a cam member is selectively positioned with respect to an inlet orifice so as to progressively restrict fluid flow through the valve unit which in turn will result in increased actuating fluid pressure being applied to activate the clutch unit. The combination of this cam type rotary control valve with the stepping motor drive arrangement provides an extremely accurate and reliable control for actuation of the clutch unit which is substantially self-cleaning so as to substantially reduce degredation of operation as a result of contaminants in the actuating fluid.
Control circuit means are also provided for controlling the operation of the stepping motor so as to enable precise control of the equipment startup and acceleration profile. The control circuit means allows the rate of acceleration to be easily adjusted to accommodate particular operating conditions and once set will insure repeatability of the acceleration rate. Additionally, provisions may also be included in the circuit means to disengage or deactuate the clutch unit in the event of abnormal operating conditions particularly during the startup period so as to prevent damage to the clutch unit such as may occur from excessive slippage thereof.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.